1. Field of the Invention
The present invention relates generally to a strip brush seal arrangement to effect a seal between a rotary shaft of a compressor, gas turbine engine, refrigerator, pump or the like, and a relatively rotating element. More particularly, this invention relates to a technical domain of strip brush seals in which a mounting portion bundling thin strips are securely attached for an improved seal capability of a seal portion and a resilient flexibility provided to the seal portion effectively prevents wear of the seal portion.
2. Description of the Related Art
Related art of the present invention is found as a strip brush seal 100 disclosed in U.S. Pat. No. 6,343,792. In the strip brush seal 100 of FIG. 15, a plurality of circular-arc thin strip brushes 109, also called “leaves”, are densely packed around the circumference of a shaft 120 in order to inhibit a flow between a high pressure region P1 and a low pressure region P2.
A plurality of the strip brushes 109 are integrally bundled at mounting portions 104 of the strip brushes 109 by means of an annularly-shaped outer perimeter surface which is defined as a soldering portion 105. The mounting portions 104 which form an annulus as a whole are installed in a groove of a housing 110. A back plate 102 is disposed on one side of the strip brushes 109 which is in the lower pressure region P2 whilst a retainer plate 103 is disposed on the other side which is in the higher pressure region P1. The back plate 102 and the retainer plate 103 provide supports on the both sides of the strip brushes 109, and the back plate 102 effects a seal against a fluid located in the higher pressure region P1. At the same time, a seal against leakage of the fluid between the back plate 102 and the rotary shaft 120 is effected by a plurality of the strip brushes 109 which are densely packed to form the annular shape.
However as the strip brush 109 is made rather rigid, the free end surface of the strip brush 109 fits with the outer diameter surface of the rotary shaft 120 with a relatively large clearance therebetween. The fit clearance makes it difficult to effect a seal against the fluid. Also the large clearance between the strip brush 109 and the rotary shaft 120 imposes another difficulty on the positional alignment of the clearance because of which assembly task of the strip brush 109 takes a long time. In addition, manufacture of the strip brush 109 not only requires cutting of a rectangular strip from a thin metal sheet of 0.1 mm thickness but also needs a uniform bending of all the strips into an identical circular-arc form along the direction of arrangement. This bending process requiring high precision is likely to increase the production cost because of the difficulty in handling of such a thin sheet material.
Furthermore soldering of the mounting portion 104 at the outer perimeter surface emits substantial heat so that it becomes difficult to achieve an accurate position of the strip brush 109 in order to keep the annularly-shaped array of the mounting portions 104. In particular, for the strip brushes 109 being piled to an annular shape in which the strip brushes 109 of uniform thickness are in use, an inter strip gap in the outer circumference region differs from that in the inner circumference region. This necessitates the use of spacer elements at the outer circumferential region to compensate the gap difference. Deployment of such spacer elements in the gaps between the individual strip brushes 109 further increases the complexity of the assembly process.
Further related art of the present invention is found as a strip brush seal 150 of another example in the same patent. The strip brush seal 150 is illustrated in FIG. 16.
Strip brush seal 150 shown in FIG. 16 has a similar arrangement to the strip brush seal 100 of FIG. 15. Differences between the strip brush seal 150 of FIG. 16 and the strip brush seal 100 of FIG. 15 are explained below. Strip brushes 180 are arranged to an annular shape in the strip brush seal 150 wherein six protrusions 180A are disposed on the surface of the outer perimeter region of the individual strip brushes 180 so that the protrusions 180A provide a certain clearance gap between adjacent strip brushes 180. The clearance gap given by the protrusions 180A, however, makes soldering at the outer perimeter surface more difficult because of the gap being present between the successive strip brushes 180. In order to alleviate this problem, mounting portions 190 located at the outer perimeter of the strip brushes 180 need to be fitted to a groove portion 160C of an annularly-shaped body element 160.
As the strip brush 180 has a rectangular shape, it is not straightforward to accurately fit the strip brush 180 to the groove portion 160C of the annularly-shaped body element 160 whose side-walls are defined by a support portion 160A and a back plate portion 160B. Also when the strip brush 180 is mounted in the groove portion 160C, both distal edge corners 180C, 180C of the strip brush 180 are apt to scratch the surface of the rotary shaft 120. In order to avoid the problem, the corners need to be made round but the nature of the thin sheet material makes it difficult.
In addition a process fluid partially leaks through the protrusions 180A toward the outer perimeter side of the strip brush 180, which further continues to leak along the groove portion 160 and reduces the seal capability after all. Also the annularly-shaped body element 160 is comprised of a plurality of circular-arc segments which are circumferentially divided in order to densely pile the individual strip brushes 180 onto the groove portion 160C. The assembly process of the individual segments to an annularly-shaped integral structure via joint surfaces becomes inevitably complex from the viewpoint of effecting a seal against the fluid because of the presence of the protrusions 180A disposed on the strip brushes 180. This in turn makes difficult the installation of the annularly-shaped body element 160 into the groove portion 160C of a housing 170. As a consequence, the overall manufacture and assembly cost of the strip brush seal 150 will increase.
In the strip brush seal 100 wherein a plurality of thin strip brushes 109 are, as described above, integrally arranged to form an annular shape, the thermal deformation of the strip brush 109 during the soldering process at the mounting portion 104 located in the outer perimeter side produces uneven arrangement of the free-end edges of a plurality of the strip brushes 109, which affects the seal capability between the strip brushes 109 and the rotary shaft 120. The soldering process is applied over the outer perimeter surface of the strip brushes 109. However, the soldering over the outer perimeter surface causes a problem that the soldering strength somewhat diminishes against the force exerted from the free-end edge of the strip brush 109. Also in case of a unit segment which consists of a plurality of strip brushes 109 welded together, a difficulty in obtaining a uniform contact at the joint surfaces of the individual unit segments causes a decline of the seal capability at the joint surfaces as well as an increase of the assembly time. Furthermore if the strip brushes 109 are densely piled with no clearance gap therebetween to form an annular body, the individual strip brushes 109 collectively behave as a solid body with little flexibility, and when the rotary shaft 120 rotates relative to the strip brushes 109 being in contact therewith, the both elements are subjected to friction against each other and prone to wear due to the friction.
In the strip brush seal 150, as another example wherein protrusions 180A are disposed on the strip surface in the mounting portion 190 of the strip brush 180, the gaps created between adjacent strip brushes 180 make it difficult to solder evenly the outer perimeter surface of the strip brushes 180 thus arranged. In order to alleviate the problem, an annularly-shaped body element 160 is employed for fixating the strip brushes 180. However fixation of the mounting portions 190 of the strip brushes 180 is quite difficult. Also the annularly-shaped body element 160 needs to be constructed as an assembly of unit segments of circular-arc. Therefore problems remain in the assembly and the seal capability at the joint surfaces between the successive unit segments.
The present invention is introduced to alleviate the above mentioned problems. A primary technical goal which this invention tries to achieve is to improve the joint strength at the mounting portion of a strip brush, to enhance the elastic deformation of the strip brush by establishing a clearance gap between the adjacent surfaces of the arranged strip brushes, and to improve the seal capability of the seal portions. Another goal is to reduce the production cost of a strip brush seal. Yet another goal is to prevent soldering or welding at the mounting portion of a strip brush seal from causing the uneven arrangement of strip brushes and to avoid the deformation of thin strip brushes due to soldering or welding.